The present invention relates to a memory fine tuning arrangement used for television tuners, and more particularly to television tuner of the type which provides a so-called pre-setting fine tuning arrangement for automatically providing a fine tuning adjustment for each individual television channel by employing the pivotally mounted member. Specifically, the present invention is directed to an improved pivotal shaft of the pivotally mounted member commonly used for both rotary and push pre-setting fine tuning devices and which is manufactured economically by plastic molding technique.
Generally, mechanical channel selecting devices for VHF television tuners are mainly classified as rotary-switching types or turret types. Turret type tuners include an incrementally rotatable channel selector shaft for selectively connecting certain ones of a plurality of tuned circuit elements for each of a plurality of channel selector positions. For clear reception in each of the channel positions of the selector shaft, it is customary to include an impedance device having an adjustable value in the local oscillator circuit. This impedance device is conventionally adjusted by means of a fine tuning shaft concentrically mounted with respect to the channel selector shaft. The fine tuning shaft is connectable by the viewer to adjust the tuning impedance for each predetermined position of the selector shaft. Various memory fine tuning arrangements have been proposed to maintain individual channel tuning adjustments once they have been established by the user without requiring adjustment of the fine tuning shaft of the tuner by the user each time a particular channel is selected. One such arrangement is the push pre-setting type fine tuning device which requires the operator to push in a control knob of the fine tuning shaft and while maintaining pressure on the knob to rotate the same to adjust a fine tuning element within the tuner, the other is the rotary pre-setting type fine tuning device which requires the operator to only rotate a control knob of the fine tuning shaft for fine tuning adjustment. These devices are particularly useful on turret type tuners having individual tuned coil assemblies or units for each channel. These coil units are removably mounted in the rotatable turret structure, and are provided individually with an oscillator coil, the inductance of which may be adjusted by means of an adjustable element which extends into an opening in the end of the coil units adjacent the oscillator coil.
Since television tuners are made in large volumes, in order to be commercially competitive, it is desirable to provide a low cost pre-setting fine tuning device with a minimum number of parts and that can be assembled in an easy and simple manner. The fine tuning device requires a mechanical arrangement for translation of rotary motion of the fine tuning shaft into rotary motion of the adjustment element, since the fine tuning shaft is offset laterally from the axis of the adjustment element in the individual coil units. Also, engagement with the adjustment element must terminate automatically when the user releases the fine tuning shaft so that the turret is free to rotate to another channel position. For example, such fine tuning devices are disclosed in U.S. Pat. No. 3,316,770 for push pre-setting type memory fine tuners and in U.S. Pat. No. 3,183,726 for rotary pre-setting type memory fine tuners. These fine tuning devices include a pivotally mounted member on the front wall of the chassis base with a coil spring between the member and the front wall to exert a bias force on the member in the predetermined direction. The pivotally mounted member is provided with a lever plate having one end pivotally mounted to the front wall of the chassis base by using a pivot pin mounted on the front wall. In this assembly, however, it is requested to mount the pivot pin at a right angle on the front wall, and to design such parts with close tolerance for maintaining a parallel relation between the lever plate and the front wall. Therefore, the lever plate generally must be made by die-casting metallic zinc, and the production cost has been materially elevated by the necessity of using expensive materials and processes.